TASK

Fix common Base64 decoding errors

Why a Base64 string fails to decode — missing padding, URL-safe alphabets, stray whitespace — and the exact steps to repair each case.

1

Base64 encodes every 3 bytes into 4 characters, so a valid string's length (ignoring whitespace) is always a multiple of 4. When a decoder reports INVALID_BASE64, one of three causes is almost always responsible.
2

Base64 Decoder →
Paste the failing string and try decoding with the standard alphabet first. The error message distinguishes invalid characters from invalid length.
3

Cause 1 — missing padding: if the length is 2 or 3 modulo 4, append '=' characters until the length is a multiple of 4. Cause 2 — URL-safe alphabet: tokens and URL parameters use '-' and '_' instead of '+' and '/'; swap them before decoding. Cause 3 — stray whitespace or line breaks: strip spaces and newlines that MIME transport may have inserted.
4

Base64 Encoder →
Round-trip check: encode a known plaintext and compare the output with your broken string character by character to spot an alphabet or padding difference.

Frequently asked questions

Why do some Base64 strings end with '='?: Padding. When the input is not a multiple of 3 bytes, one or two '=' characters are appended so the output length is a multiple of 4. Padding can sometimes be inferred, but strict decoders require it.
Is Base64 encryption?: No. Base64 is a reversible encoding with no secret. It is used to transport binary data through text-only channels, never to protect it.

Workflows that solve this

Convert Ascii85 to Base64

Decode Ascii85 and re-encode as Base64 for wider compatibility.

Convert Base2048 to Base64

Decode Base2048 (emoji) and re-encode as Base64 for standard transport.

Convert Base32 to Base64

Decode a Base32-encoded string into raw bytes and re-encode as Base64 for more compact representation.

Convert Base58 to Base64

Decode Base58 and re-encode as Base64 for standard compatibility.

Base64 encode then decode round-trip

Encode text to Base64 and decode it back to verify the round-trip preserves the original data.

Convert Base64 to Base85

Decode Base64 and re-encode as Base85 for compact representation.

Convert Base64 to Hex

Decode a Base64 string into raw bytes and re-encode it as hexadecimal for inspection or interop.

Blowfish Encrypt then Base64

Blowfish encrypt then Base64-encode for text-safe transport.

Decode a Basic Auth credential pair

Decode the Base64 portion of an HTTP Basic Authorization header into username:password.

DES Encrypt then Base64

DES encrypt then Base64-encode for legacy compatibility.

Encode a JSON payload for URL transport

Prepare a JSON document for a URL parameter: pretty-print, Base64-encode, then percent-encode — the exact inverse of the nested-parameter decode chain.

AES encrypt then Base64 encode

Encrypt plaintext with AES and encode the ciphertext as Base64 for text-safe transport.

Hash content and encode as Base64

Compute a hash of the input and encode the hash digest as Base64 for compact transport.

Convert Hex to Base64

Decode a hexadecimal string into raw bytes and re-encode it as Base64 for compact transport.

HMAC Sign then Base64 Encode

Generate HMAC signature then Base64-encode for API auth headers.

Morse Encode and Base64 Transport

Encode text as Morse code then Base64-encode for digital transport.

Decode and format a JWT payload

Parse a JWT token, extract its payload, and format the JSON for inspection.

RC4 Encrypt then Base64

RC4 encrypt then Base64-encode for transport.

RIPEMD-160 Hash then Base64

Compute RIPEMD-160 hash then Base64-encode for transport.

Shuffle Text and Base64 Encode

Shuffle text characters then Base64-encode the result.

Unicode Escape and Base64 Encode

Unicode-escape text then Base64-encode for ASCII-safe transport.

URL Encode then Base64 Double Encode

URL-encode then Base64-encode for double encoding in API payloads.

Decode nested URL parameter (Base64 JSON)

Unwrap a URL parameter that carries URL-encoded Base64 JSON into readable, formatted JSON.

UUencode then Base64

UUencode text then Base64-encode the result for double encoding.

Generate UUID and Base64 Encode

Generate a UUID then Base64-encode it for compact storage.

Learn more

Want to understand why?

Base64: how it works and when to use it

The byte-to-character mechanics behind Base64, why padding exists, which alphabet variants you will meet, and the boundaries where Base64 is the wrong tool.

How to Base64 Decode Text

Learn to reverse a Base64 string back to its original form, including how to handle padding and invalid characters.

Base64 maps arbitrary binary data onto 64 printable ASCII characters (A-Z, a-z, 0-9, +, /) so that binary data can travel over text-only channels.

Base64 Padded (PH)

Base64 Padded denotes the standard Base64 variant that strictly keeps its = padding characters, so the output length is always a multiple of 4.

Related tools

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